Was wondering if there's performance difference between SSDs using own more agressive automatic garbage collection or relying to TRIM command to activate garbage collection when used as Smart Response Tech cache drive?

As TRIM is function of OS/file system SSDs used for this kind non OS based Smart Response/Rapid Start etc use probably behave quite differently. Data probably being not removed until it gets overwritten also surely has effect.

(apparently cache is just special partition and drive should be accessible normally by manufacturer's tools for like firmware update?)

And with everything increasing in size constantly is that 64GB cache max size just software limit decided years ago or hardware limit?

SSD space is such expensive that I would prefer installing for example games to big RAID1 HDD storage volume with decent amount of most played games staying in cache. As disk accesses of games are almost completely reads they should be easy targets for caching.

Intelligent RAID algorithm could nearly double read speed of bigger sequential accesses with RAID1 by balancing load between disks and if it can't do load balancing then performance should always be at level of single disk and never below it by reading from single disk. (unless first disk hits error there's no need to read data again from second)

The technology behind Intel® Smart Response technology cache acceleration is RAID 0, in that case, proprietary drive manufacturer's tools may not recognize the drive, you would need to evaluate that using the tool to check.

The 64 GB is a limitation of the implementation of the feature itself, however by now there is no information if this will be increased in the near future.